This invention relates generally to molding an article with material, and more particularly concerns an injection control gate for controlling the flow of moldable material into a mold for molding an article.
The use of plastic components in machines, equipment and generally in commercial products is wide, extensive and continually growing. Plastic components afford low cost, lightweight corrosion resistance and many other significant advantages.
The manufacture of plastic components is typically accomplished through a molding process. The molding process includes injecting plastic material in the form of small pellets into a machine which includes a mold having a cavity with the shape of the plastic component. The plastic pellets are conveyed into a cavity or chamber and are advanced toward the cavity of the mold by a screw or ram. The screw or ram is housed in an electrically heated enclosure which melts the pellets into a liquid which readily fills the cavity within the mold.
The mold typically includes a fixed and movable portion with the cavity being formed therebetween. The movable portion of the cavity is separated from the fixed portion after the cavity is filled with the plastic fluid and allowed to cool. The cooled plastic,material thus forms the molded plastic part.
The plastic liquid within the screw or ram is introduced into the mold cavity through channels or runners in communication between the screw of ram and the mold cavity. To regulate the flow of the plastic material through the channels or runners, valves typically called gates are positioned within the channels or runners and are opened to permit flow of the plastic fluid therethrough and closed to prohibit the flow of the fluid.
The opening and closing of the gates within the channels or runners is an important part of the development of a proper process for molding plastic parts. This is particularly true for large and flat complex components which may have a large number of channels or runners and consequently a plurality of gates.
Typical problems in the filling of the plastic fluid within the mold cavity are fill balancing and clamp tonnage optimization. In fill balancing, it may be necessary to have more fluid pass through a channel in a area within the mold cavity which has a large area or mass and to permit only a much smaller amount of plastic fluid to flow through a channel related to a portion of the mold cavity where the mass or cross section is quite small.
Further, in order to optimize, i.e. minimize, the clamp tonnage which is the pressure or force required to clamp the mold or cavity halves together against injection pressure. Clamp tonnage is best minimized when the flow of the plastic material through the channels or runners corresponding to portions of the cavity are evenly balanced and much higher amounts of material are not necessary to be filled within only one particular gate which corresponds to that area of high volume. Thus optimum flow of material through the proper channels or runners for the proper period of time may minimize the amount of injection pressure or force required to fill the mold cavity with liquid plastic, and thus reduce clamp tonnage requirements.
Furthermore, as the liquid plastic enters the mold cavity from different channels or runners, the molded material meets at a transition zone within the cavity. The integrity and appearance of the plastic material at this transition zone may be inferior to other portions of the plastic material within the mold cavity. For example, the transition zones may occur at highly visible areas where the appearance of the molded article is more important or in areas of greater stress within the molded article where material integrity is more critical. Thus, it is important that the flow of material into the mold be accurately and precisely controlled.
While generally it may be sufficient to open and close a gate within a channel or runner only once during the molding cycle, at times it may be desirable to open and close different gates at different times within the molding cycle, or a particular gate more than once. In situations where material is passed through a first channel with a first gate into an area of small cross section while additional material is permitted to flow through a second channel and a second gate into a area of large cross section, the area of greater cross section typically requires a much large amount of time to fill the large cavity. Thus, the first channel with the small cavity area has its gate shut before the second gate of the large area is shut.
The material flowing through the first channel then tends to cool after it has flowed and may cause a problem since the gate, which is now shut cannot transmit hold, or pack pressure to the minor area. The material in this area will shrink away from the cavity wall during the hold phase of the molding cycle if hold pressure cannot be applied. This will render the molded article unusable dimensionally and cosmetically. If, however, the first gate which regulates the first channel is permitted to be opened again for a short period of time immediately preceding the end of the molding cycle, pressure through the first channel may cause the molded material through the first channel to transmit hold pressure through the molded article and avoid an unacceptable article.
Typically, molding machines either have no capability whatsoever to regulate gates within a mold of the plastic molding machine, or include only the ability of opening all the gates and closing all the gates simultaneously. Other newer machines may have some limited ability to sequence gates but may be limited to a time variable singular sequence for each injection gate within the molding cycle.
Newer, modern, more expensive machines such as those manufactured by Engel Manufacturing Company, Guelph, Canada, Model No. 600/200 VHRO, have the ability to sequence the opening and closing of gates within a molding machine. These machines are able to open and close a particular gate once during the molding cycle. Recently, Incoe Corporation has offered a gate sequencing control system for opening and closing the valves of a mold for a molding machine. The Incoe system is portable computer based system and is very complicated and expensive.
The following disclosures nay be relevant to various aspects of the present invention:
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,523,045 discloses methods for injection molding and injection blow-molding multi-layer plastic articles, including containers and partisans for forming containers, which include providing a plurality of co-injection nozzle means for injecting plastic materials into associated injection cavities to form each article, providing streams of polymeric materials to form corresponding layers of the articles, moving each stream separately to plural nozzle means, separately receiving the streams in the plural nozzle means, and injecting the streams to form the multi-layer plastic articles. Preferably, each stream of material which is to form a corresponding layer of the articles is provided with substantially the same polymer flow, preferably from where each stream is split and moved to each nozzle means. Valve means can be employed in each nozzle means for positively controlling preferably substantially simultaneously the flow and nonflow of respective materials into the central channel of the nozzle means. Preferably, injection is effected to provide uniform onset flow of one or more internal layer materials into the central channel, cause foldover of one or more of the internal layers and provide in the parison or container sidewall one or more internal layers whose leading edge is substantially unbiased relative to the terminal end of the sidewall.
U.S. Pat. No. 5,149,547 discloses apparatus and methods suitable for controlling and metering thermoplastic material or resin to multiple cavities of dissimilar volume, such as a family mold is described, whereby the amount of resin injected into each cavity can be individually controlled. This system minimize overfilling or underfilling of individual article cavities in such a multiple cavity tool and, therefore, allows for the production of more uniform plastic articles from a multiple cavity mold or tool. In practice, a spindle, which is designed to rotate in a reproducible manner as resin flows past it, is inserted into the resin stream feeding each cavity. The amount of resin fed to a particular cavity is determined by measuring the rotation of the spindle. When the amount of resin fed to a particular cavity is equal to the amount appropriate for that cavity (the target amount), the shut-off valve associated with that cavity is activated, thereby terminating the resin flow to that cavity without affecting resin flow to the other cavities. Resin flow is continued until all cavities are filled with their respective target amounts of resin. The apparatus and methods of this invention are especially adapted for use in gas-assisted injection molding using multi-cavity equipment.
U.S. Pat. No. 5,141,696 discloses an engagement for mechanically adjusting the flow through each of a plurality of mold nozzles supplied by a manifold for a multi-cavity mold, to properly balance the flow into each mold cavity. The arrangement includes a converging opening located immediately upstream of the cavity gate opening and receiving a pin extending through the main feed passage. The position of the pin is axially adjustable by having a threaded head received in a threaded bore formed in the manifold, with a pressure sealing bushing received over the pin stem. The flow of material can be balanced by externally adjusting the position of the pin associated with each mold nozzle. A side accessible arrangement is provided in a second embodiment, in which a worm gear drive connects a transversely arranged cross rod to the adjustment pin.
U.S. Pat. No. 5,078,589 discloses an arrangement is disclosed for independently controlling shutoff and flow to a cavity gate in a multi-cavity injection mold apparatus, in which a plurality of valve pins are mounted to a movable holder plate, each aligned with a cavity gate and movable thereinto to control shutoff and a plurality of fixed position plunger sleeves are each mounted over a respective valve pin and adjustably positioned with respect to a restriction feature in the supply passage upstream of the associated gate.
U.S. Pat. No. 4,592,711 discloses an apparatus for injection molding plastic parts. The method includes the step of melting and pressurizing plastic material, directing the molten pressurized plastic material into passages leading to a mold, a selectively opening shut-off valve disposed along the passages, selectively closing the shut-off valve after a predetermined amount of molten pressurized plastic material has entered the mold and cooling the predetermined amount of molten pressurized plastic material in the mold to form a part. The apparatus includes an extruder providing pressurized molten plastic material, a mold adjacent the extruder, passages interconnecting the extruder with the mold, and a selectively operable shut-off valve disposed along the passage.
U.S. Pat. No. 4,279,582 discloses a method and apparatus for multiple cavity injection molding which permits individual variation of gate opening time for mold shut-off bushings. The gate pins for the shut-off bushings are controlled by individual double-acting fluid motor, the bushings being fed by a common manifold. Gate opening is thus not dependent upon attainment of a predetermined injection pressure. Closure of the gate for each cavity will permit material to be fed faster to the other cavities. Novel means is provided for securing each gate pin to its actuating cylinder, which minimizes heat transfer to the motor, accommodates expansion of the material manifold and permits gate opening adjustment. The fluid motors are end-mounted on an actuating fluid manifold, allowing close juxtaposition. A cycle counter may be used to control inventory.
U.S. Pat. No. 4,140,238 discloses a nozzle shut-off valve for injection molding machine for plastic material, especially thermoplastic material, has two pneumatic cylinder-and-plunger units. One such unit has its plunger mounted to reciprocate so as to block the passageway of the plastics through the nozzle. The first such plunger and cylinder unit is provided with a pilot passage in the valve nozzle so that the pressure of molten plastic can be used to open it. The second such unit is much smaller diameter and has its plunger mounted to block the pilot passage so that the second unit in effect becomes a pilot valve and controls the application of fluid pressure through the pilot passage to the first unit plunger or blocking plunger.
U.S. Pat. No. 3,902,665 discloses an extruder shut-off nozzle with a valve body and orifice having a plurality of metering ports feeding the nozzle passageway. A closure member captive in the body of the torpedo capable of being moved by compressed air after an injection cycle to seal the extruder orifice and prevent drooling of plasticized material at the nozzle when starting the next mold cycle. A suck-back action of the extruder screw at completion of the injection cycle will cause melt normally in the nozzle to be pulled back into the extruder chamber, thereby preventing drooling of plastic from the nozzle when the piston is in the shut-off position.
xe2x80x9cControl Cavity Filling with Melt xe2x80x98Throttlesxe2x80x99 in the Moldxe2x80x9d discloses a dynamic feed system for an injection molding machine. By adjusting an array of melt-flow throttle valves, closed loop pressure control is in the tool, rather than in the machine.
Incoe Corporation internet listing discloses a gate sequencing Control system for controlling the opening and closing of pneumatic or hydraulic valve gates and provides up to 40 gate sequences. The activation of the gates may be based on screw position, time or a combination and gates may be reopened if desired.
All of the above references are hereby incorporated by reference.
In accordance with one aspect of the present invention, there is provided an apparatus for sending a switching signal to a switching device for switching the position of an injection gate of a injection molding machine for molding a work piece in a mold during a molding cycle between an open position and a closed position. The switching signal is indicative of one of the open position and the closed position. The apparatus is to be hand carried by a machine operator. The apparatus includes a frame including a portion thereof for gripping by the operator and a power supply operably associated with the frame. The apparatus also includes a timer operably associated with the frame. The timer is operably connectable to the power supply for receiving an initiation signal from the injection molding machine indicative of the initiation of the molding cycle and for generating the switching signal in response to the initiation signal. The apparatus also includes an input conduit operably associated with the frame for transmitting the initiation signal toward the timer and an output conduit operably associated with the frame for transmitting the switching signal toward the switching device.
Pursuant to another aspect of the present invention, there is provided a method for switching the position of an injection gate of a injection molding machine for molding a work piece in a mold during a molding cycle between an open position and a closed position in response to a switching signal from the machine. The switching signal is indicative of one of the open position and the closed position. The method includes the steps of providing a hand carried portable control unit for switching the position of the injection gate, receiving at the portable control unit an initiation signal from the molding machine indicative of the initiation of a molding cycle, positioning a timing delaying device including a timer in the portable control unit, selecting a time delay for the timer within the timing delaying device, initiating the timer by receiving the initiation signal at the timing delaying device, waiting for the time delay of the timer to elapse, and transmitting a switching signal to the injection molding machine for switching the position of the injection gate to one of the open position and the closed position after the delay time has elapsed.
Pursuant to yet another aspect of the present invention, there is provided an article made by a injection molding process including switching the position of an injection gate of a injection molding machine for molding a work piece in a mold during a molding cycle between an open position and a closed position in response to a switching signal from the machine. The switching signal is indicative of one of the open position and the closed position. The process includes the steps of providing a hand carried portable control unit for switching the position of the injection gate, receiving at the portable control unit an initiation signal from the molding machine indicative of the initiation of a molding cycle, positioning a timing delaying device including a timer in the portable control unit, selecting a time delay for the timer within the timing delaying device, initiating the timer by receiving the initiation signal at the timing delaying device, waiting for the time delay of the timer to elapse, and transmitting a switching signal to the injection molding machine for switching the position of the injection gate to one of the open position and the closed position after the delay time has elapsed.